The invention relates to a hydraulically supported power steering system, in particular for motor vehicles. A double-acting hydraulic displacement unit is provided for generating an auxiliary hydraulic force. Controllable hydraulic pressure is supplied to and relieved from displacement body working spaces by means of associated conduits controlled by a servo-valve. Damper valves are arranged on the conduit connections.
In order to restrict the actuation forces which have to be applied by the driver of a motor vehicle when actuating the vehicle steering, heavy vehicles are regularly equipped with a power steering system which, at least in the case of passenger cars, typically operates by means of auxiliary hydraulic force which is generally generated by means of a displacement unit configured as a piston/cylinder unit.
In addition, vehicle steering systems regularly have a separate steering damper which suppresses vibrations excited in the steering system as required.
In this connection, it is basically known from German Patent Document DOS 40 29 156 to allow the double-acting piston/cylinder unit used for generating the auxiliary hydraulic force to act also as the steering damper by arranging damper elements in the conduits between the servo-valve and this unit. These damper elements, however, have a relatively complicated construction.
A similar arrangement is the subject matter of German Patent Document DOS 41 06 310.
It is known from German Patent Document DOS 29 27 039 to arrange a non-return valve, provided with a throttling passage hole and opening towards the respective piston working space, on the cylinder-end connection of each of the conduits which connect the servo-valve to the double-acting piston/cylinder unit of a power steering system. The valve housing of the non-return valve can be formed by a bolt which is used for fixing the respective conduit to the cylinder.
These known constructions have not been generally applied in practice, although it is fundamentally advantageous to obviate a separate steering damper and to integrate its function in the power steering system.
In practice, therefore, separate steering dampers are inserted, such as are described, for example, in the publication REIMPELL, J.: Fahrwerktechnik: Lenkung, VOGEL-BUCHVERLAG WURZBURG, 1st Edition 1984, Pages 119 to 127. In these, the pistons of the steering system dampers typically have axial passages which are controlled by plate valves arranged on the piston.
An object of the invention is to improve the construction of a power steering system of the type referred to above and to permit good matching of the damper forces.
This object is achieved according to the invention in that the damper valves have a perforated disc type of support part which can be clamped in the manner of a spacing ring or washer between a bearing surface of a connecting mouthpiece arranged on the housing of the servo-valve or of the displacement unit and an opposite bearing surface of a connecting part of the conduit, which connecting part can be connected to the connecting mouthpiece.
In preferred embodiments of the invention, provision is particularly made for the support part to have a disc-type piston with axial passages controlled by the damper valves and this piston divides two chambers from one another within a space enclosed by the connecting mouthpiece and the connecting part, of which chambers one is connected to the respective conduit and one is connected to the servo-valve or a working chamber of the displacement unit or piston/cylinder unit.
In the invention, the assembly requirements are, on the one hand, kept very small because the arrangement of the damper valves is undertaken in the simplest manner during the assembly of the connecting conduits between the servo-valve and the displacement unit or piston/cylinder unit.
On the other hand, the arrangement of the damper valves on a disc-shaped piston achieves the effect that elements known from the manufacture of steering dampers can, fundamentally, be employed unaltered.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.